The invention relates to a gate valve with a housing, with two seat rings arranged in the housing and two valve plates which are arranged between the seat rings and which can be brought into bearing contact with the two seat rings via an actuating device, the valve plates being arranged on a plate holder so as to form a wedge shape.
Gate valves of this type are generally known and are employed in many sectors.
German Patent document DE 1 230 279 B discloses a gate valve with valve plates arranged in a wedge-shaped manner and connected tiltably to one another, in which the valve plates cooperating with seats in the housing are supported on the valve via a plurality of springs which are distributed over the circumference of the valve plates and which are prestressed by means of hexagon screws extending through the springs, in such a way that the valve plates come to bear against the seats only shortly before their end position is reached. A specific force and a specific travel are predetermined via the hexagon screws.
However, as a consequence, the valve plates, after being lifted off from the seat rings, may shift out of place and consequently rattle. The result of the undesirable shift of the valve plates may also be, when the valve is closed again, that the sealing faces of the seat rings or the sealing faces of the valve plates are damaged. Moreover, arranging a large number of springs over the circumference of the valve plates is highly complicated and costly. Due to the large number of springs, the orientation of the valve plates does not correspond to the ideal setting on account of the tolerances involved.
The object of the invention is to provide a cost-effective and reliably operating gate valve which is capable of sealing off both high and low differential pressures, without the gate valve being moved into a position in which the valve plates become wedged together.
The object is achieved, according to the invention, in that each valve plate has, on the side facing the other valve plate in each case, a depression in which in each case a pressure piece is arranged, each pressure piece having a recess on the side facing the other pressure piece in each case, the two recesses together forming a space which accommodates a cup spring assembly comprising a plurality of cup springs, in each case with a first spring force and with a first spring travel, and a plurality of cup springs, in each case with a second spring force and with a second spring travel, and the first spring force being higher than the second spring force and the first spring travel being shorter than the second spring travel.
By two cup spring constants being combined, one for high forces and short travels and the other for low forces and long travels, it is additionally possible, at the transfer point at which the guidance of the valve plates changes over from the seat rings to the plate holder and guide devices, for example lateral strips or a groove in the housing, to achieve a high spring force for sealing off the valve plates when differential pressures between fluid inflow side and fluid outflow side are low. The high force occurs only at the very last moment of the closing operation. Before that, the cup springs give rise to only a relatively long travel with a relatively low force. The low force also means that there is much lower friction on the seat rings and the valve plates. Moreover, the low force enables the valve plates to be locked manually in the plate holder.
In a further refinement, the pressure pieces have in each case a shape essentially in the form of a segment of a sphere, with a curved face and with a plane face lying opposite the curved face.
According to the invention, the depression formed in each of the valve plates has a shape complementary to the shape in the form of a segment of a sphere of the respective pressure piece.
By the shape of the pressure pieces being essentially in the form of a segment of a sphere and because the shape of the depression, into which the respective pressure piece is inserted, is complementary thereto, the pressure pieces are always seated in the depressions of the valve plates so as to be oriented optimally with respect to one another.
Since a bore extends from the bottom of the recess, provided on the plane face of one of the pressure pieces, to the curved face of the pressure piece, and a pin extends from the bottom of the recess, provided on the plane face of the other pressure piece, into the bore of the first-mentioned pressure piece, an optimal transmission of force from the cup spring assembly to the pressure pieces is made possible.
For an operationally reliable behavior of the wedge-type valve, the dimensions of the cup springs with the lower spring force and with the longer spring travel are designed in such a way that said cup springs can be pressed together into a block without any settling behavior.
Ideally, the spring forces of the cup springs with the high spring force are dimensioned in such a way that these act upon the end faces of the seat rings only when the gate valve is in the completely or almost completely closed position, thus resulting in much lower friction on the seat rings and the valve plates.
Advantageously, the spring forces of the cup springs are designed in such a way that the required surface pressure upon the seat is applied by means of the cup spring forces when differential pressures are low, thereby ensuring that the gate valve shuts off reliably.
Other objects, advantages and novel features of the present invention will become apparent from the following detailed description of one or more preferred embodiments when considered in conjunction with the accompanying drawings.